There are many kinds of burglar alarms for installation in vehicles. Most of them are powered by the vehicle's main battery, and will not function if said main battery is damaged or disconnected. Moreover, forgetting to turn off the ignition switch or the headlights before leaving the vehicle will deplete the battery, but there may be no warning to the owner of this situation. In view of the above defects, the inventor has created a main battery disconnection alarm and headlight warning circuit.